It is often necessary to quickly obtain a sample of blood and perform an analysis of the blood sample. One example of a need for obtaining a sample of blood is in connection with a blood glucose monitoring system, which a user must frequently use to monitor the user's blood glucose level.
Those who have irregular blood glucose concentration levels are medically required to regularly self-monitor their blood glucose concentration level. An irregular blood glucose level can be brought on by a variety of reasons including illness such as diabetes. The purpose of monitoring the blood glucose concentration level is to determine the blood glucose concentration level and then to take corrective action, based upon whether the level is too high or too low, to bring the level back within a normal range. The failure to take corrective action can have serious implications. When blood glucose levels drop too low—a condition known as hypoglycemia—a person can become nervous, shaky, and confused. That person's judgment may become impaired and that person may eventually pass out. A person can also become very ill if their blood glucose level becomes too high—a condition known as hyperglycemia. Both conditions, hypoglycemia and hyperglycemia, are potentially life-threatening emergencies.
One method of monitoring a person's blood glucose level is with a portable, hand-held blood glucose testing device. The portable nature of these devices enables the users to conveniently test their blood glucose levels at anytime or in any place the user may be. The glucose testing device includes a test sensor to harvest the blood for analysis. Such a test sensor is described in U.S. Pat. No. 5,759,364, which is entitled “Electrochemical Biosensor.” In order to check the blood glucose level, a drop of blood is obtained from the fingertip using a lancing device. The blood drop is produced on the fingertip and the blood is harvested using the test sensor. The test sensor, which is inserted into a testing unit, is brought into contact with the blood drop. The test sensor draws the blood to the inside of the test unit which then determines the concentration of glucose in the blood. Once the results of the test are displayed on a display of the test unit, the test sensor is discarded. Each new test requires a new test sensor.
One problem associated with some lancing and/or testing devices is that the requisite amount of blood for accurate test results is not always obtained. Roughly thirty percent of lances do not produce enough blood for analysis. The amount of blood obtained from each lance varies between zero and ten microliters. For an accurate result, at least two microliters of blood must be obtained. If less than this amount is obtained, the test results may be erroneous and a test sensor is wasted. More serious an issue, however, is that the user may be relying on inaccurate results when an insufficient sample volume is harvested. Obviously, because of the serious nature of the medical issues involved, erroneous results are to be avoided.
Another problem associated with conventional lancing devices is that there is no mechanism to let the user know whether the correct amount of blood has been obtained for accurate analysis. Typically, the test units come with instructions graphically illustrating the size of the blood drop required for accurate testing. However, this visual comparison is subjective and often produces inconsistent results. To insure the requisite amount of blood is produced, users often overcompensate by squeezing or otherwise manipulating their finger to produce a larger than necessary drop of blood. However, this adds time to the overall testing process and also results in an increased amount of wasted blood. It is preferable to require/obtain as little of the user's blood as possible for accurate results. Put another way, it is desirable to only obtain the required amount of blood. Often, requiring an increased amount of blood translates into a more “invasive” procedure meaning that the obtaining of the same can take more time and be more painful. Accordingly, their exists a need for a blood glucose testing device having an underfill detection system that can determine whether a correct blood sample volume has been obtained.